Our famous Great Barrier Reef is a barrier in every sense of the word. As well as providing a haven for coastal marine life, the growing coral reef, now 2300 kilometres long, has increasingly served to protect coastal areas from tsunamis caused by underwater landslides.
New evidence, unearthed by Sydney scientists, reveals that a submarine landslide, seven kilometres wide, occurred between 20,000 and 14,000 years ago that caused a tsunami almost three metres high on the coastline between today's Airlie Beach and Townsville.
The research, published in the journal Marine Geology, shows that in the distant past, the Barrier Reef was a fringing reef that offered relatively little protection to tsunamis.
"When it was a fringing reef, the coast was much closer to the source of tsunamis," said lead researcher Associate Professor Jody Webster of Sydney University.
Could similar landslides under the sea occur at any time – and without forewarning? "There is a relatively low chance that a similar submarine landslide with the potential to cause a tsunami of up to three metres or more would happen today," Associate Professor Webster replied. "But, if one did occur, our findings suggest that the Great Barrier Reef is doing us a great service because of its ability to absorb some of that potential wave energy."
Working with Dr Jon Hill from the University of York, the scientists created simulations of the tsunami impact at today's sea level, as well as when the ocean was 70 metres lower. This is where the coastline sat before receding to its current position and was replaced at the shelf edge when the Barrier Reef formed.
"Our research suggests the Barrier Reef's health may be an important factor in reducing the impact of future tsunamis," Associate Professor Webster said.
In years to come, might the effects of global warming, ocean acidification and coral bleaching diminish the reef's effectiveness as a barrier to tsunamis?
"Our future work will try to answer these questions," he said. "In particular, we'd like to know how much energy would be absorbed and how much damage could be done by rising sea levels and tsunamis or king tides."
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